This invention relates to improvements in a method of manufacturing a fine multi-filamentary Nb-Ti based superconducting wire consisting of a Nb-Ti alloy containing one or more metal elements selected from a group consisting of hafnium, tantalum and tungsten.
Heretofore, superconducting wires have been thought to be used at 4.2 K. (i.e., the boiling temperature of helium at 1 atm.), and their properties only at 4.2 K. have been significant. Accordingly, it has been a main practical idea to use Nb-Ti binary alloy wires as superconducting wires for magnets providing magnetic field of at most 8 or 9 teslas while using compound wires of Nb.sub.3 Sn or V.sub.3 G.sub.a having satisfactory properties as superconducting wires for magnets providing magnetic field in a range of 9 to 13 teslas.
However, in accordance with increase in size and magnetic field intensity of the superconducting magnet, the superconducting wire is subject to a greater electromagnetic force, with the result that the stress damage done to the properties of the compound superconducting wire has become a serious problem. On the other hand, marked progress has been achieved recently in the field of cooling technique, e.g., pressurized superfluid helium cooling under pressure, making it possible to achieve a temperature less than 4.2 K. easily. Under the circumstances, the technique of adding another element to a Nb-Ti superconducting wire and using said superconducting wire under temperatures lower than 4.2 K., particularly, within a superfluid helium temperature range, has come to attract attentions in this field as a measure for solving the stress damage problem and obtaining a magnet generating a high magnetic field. The NbTi based alloy has a superior stress tolerance, and there is a theoretical forecast that addition of heavy elements such as hafnium, tantalum and tungsten to a Nb-Ti alloy permits an upper critical magnetic field higher than that of Nb-Ti binary alloy to be attained in the superfluidity temperature range of helium, and extensive experiments have been conducted on bulk materials of such alloys. High superconducting performance properties, however, cannot be obtained by merely thermally treating Nb-Ti based alloys as noted above, and there has been a demand for establishing a method of manufacturing a Nb-Ti based superconducting wire having a sufficiently high current carrying capacity as practical superconducting wire.